drm/dp_mst: Set CLEAR_PAYLOAD_ID_TABLE as broadcast

[Why & How]
According to DP spec, CLEAR_PAYLOAD_ID_TABLE is a path broadcast request
message and current implementation is incorrect. Fix it.

Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210224101521.6713-3-Wayne.Lin@amd.com